For the sake of the coalition, Cameron owes it to Clegg to at least deliver a referendum, so he must quash this backbench dissent. It won’t be a case of rounding-up the usual suspects; the rebellion has spread to the Tory left and loyalists - Richard Ottaway and Robin Walker have both signed. With Labour in opportunistic support, Bernard Jenkin, leader of the Tory rebellion, has the numbers to derail the bill. Aside from smoozing ad nauseam in Commons tea rooms, Cameron has an easy option: split the opposition by re-writing the bill. Detach the boundaries changes clauses from the AV bill, and then re-introduce them in a separate bill. That said, the Tory rebels have a point: constitutional changes of this import should not be binding unless turnout exceeds a minimum, and constitutional matters should be considered in isolation from local elections. Clegg should make the concessions to ease the bill's progress.